A wide range of hydride gases are used to make materials for semiconductor devices. As these devices continue to increase in complexity and precision, the purity requirements for the starting materials that are used to make them has also increased.
Metal hydrides such as silanes (i.e., hydride gases of silicon) are used in a variety of semiconductor fabrication processes, including epitaxial growth of silicon metal films to make silicon wafer substrates. In vapor-phase epitaxy (VPE) gases of silicon halides and/or silicon hydrides (silanes) are chemically decomposed on a substrate surface to deposit silicon metal and vapor-phased exhaust products such as hydrogen gas (H2) and hydrogen halides (e.g., HCl(g) when the silicon precursor is a silicon chloride).
During the growth of the silicon layer by VPE, moisture levels are carefully monitored and controlled. Unlike chemical vapor depositions of silicon dielectric films like silicon oxide, even relatively low levels of moisture contamination is problematic for silicon VPE because the oxidation of a silicon metal film has a much larger adverse impact on the film's electrical characteristics. Water vapor is one of the most common, and yet most difficult impurities to remove from process gases like silanes. Most drying processes try to reduce the moisture levels in the silane to a parts-per-million (ppm) range. However, silicon VPE processes for making silicon films for modern semiconductor and electronic components more often require reduced moisture levels in the tens to hundreds parts-per-billion (ppb) range.
Unfortunately, the delivery of ultra-high purity silane gases with low levels of moisture contaminants faces a number of challenges. Moisture and other contaminants in silanes can come from the fabrication of the source gas itself, as well as during the subsequent packaging, shipment, storage, and handling of the gas. While the silane gas manufacturer typically provides a contaminant analysis when the gas leaves the production facility, these purity levels often change as additional contaminants are introduced from outgassing by the containers (e.g., gas cylinders), as well as leaks and residual contaminants present in downstream delivery equipment.
The presence of moisture in the ambient atmosphere provides many opportunities for moisture to contaminate highly pure silanes and other metal hydrides before reaching their point of end use. Thus, there remains a need for methods and materials to purify metal hydrides such as silanes to a point where they are acceptable for use in modern electronic and semiconductor manufacturing processes. This and other problems are addressed by embodiments of the present invention.